There are many fluid components that require a desired distribution, generally equal, of a fluid flow among multiple flow paths from a common fluid flow source. One example of such fluid flow components are heat exchangers, and particularly heat exchangers that act as evaporators or vaporizers. Because the heat absorbed by the liquid fluid that is being evaporated or vaporized is mostly latent heat, it is typical for the majority of length of such vaporizing heat exchangers to be occupied by a two phase fluid. Unlike some heat exchangers, for example condensers, the flow distribution in the vaporizers is not self-correcting and different flow conditions can produce the same pressure drop (i.e., high mass flow with low quality change or low mass flow with super heat) and can therefore coexist in parallel flow paths. This can result in heat fluxes that vary significantly from flow path to flow path (i.e., from tube to tube) and can negatively affect performance and stability in the vaporizer. 
One very specific example of vaporizers are those that are used in the fuel processing system for Proton Exchange Membrane (PEM) fuel cells wherein a gaseous mixture of water vapor and hydrocarbon are chemically reformed at high temperature to produce a hydrogen-rich flow stream commonly referred to a reformate. To produce this high temperature water vapor and hydrocarbon stream, it is typical to either produce steam from liquid water for the humidification of a gaseous hydrocarbon fuel, such as methane, or to vaporize a water and liquid hydrocarbon mixture. Often, the heat source for vaporization is a hot gas, such as the reformate or combusted anode tail gas, which is already present in the fuel cell system and has substantial heat available for the required vaporization of the liquid water and/or liquid hydrocarbon. In order to make the vaporizing heat exchanger as compact as possible, it is known to flow the fluid to be vaporized in multiple parallel flow paths or passages in order to maximize the surface area to which the fluid is exposed within a given volume. The multiple parallel flow paths require that the liquid phase fluid entering the heat exchanger be distributed evenly among the parallel flow paths. While there are vaporizers suitable for use in such systems, there is always room for improvement. For example, some such vaporizers do not lend themselves to be readily or easily manufactured from a variety of materials, such as out of aluminum. One such solution has been proposed by Reinke et al in U.S. application Ser. No. 10/145,531, filed May 14, 2002 and published as US-2003-0215679 Al which shows a brazed stainless steel, stacked-plate type of heat exchanger. According to this proposal, an inlet section is provided by overlapping a pair of slotted  sheets with each sheet having very narrow slots that provide a relatively high pressure drop to each of the parallel flow path in the remainder of the heat exchanger, which results in good distribution of the fluid flow among the parallel flow paths. However, because larger amounts of brazing alloy would tend to clog the narrow channels or slots in the sheets, this construction does not easily lend itself to some materials, such as aluminum, that require a larger amount of brazing alloy in comparison to stainless steel.